An engine may be operated with one or more dedicated EGR cylinders (e.g., a cylinder that directs at least a portion of its exhaust flow, without exhaust from other cylinders, to provide external EGR to engine cylinders) that direct all of their exhaust gas to the intake air of other engine cylinders as external exhaust gas recirculation (EGR). Such an arrangement may allow the engine to operate with higher levels of exhaust gas dilution. Consequently, engine pumping work may be reduced and engine efficiency may be improved. However, an engine that includes such a passage may not respond as desired to requests for increased engine torque output because charge dilution may limit or reduce engine torque.
The inventors herein have recognized the above-mentioned disadvantages of operating a highly diluted engine and have developed an engine operating method, comprising: reducing exhaust flow of one or more dedicated EGR cylinders providing external exhaust gas recirculation to cylinders of an engine in response to an increase in driver demand torque.
By reducing exhaust flow of dedicated EGR cylinders providing external exhaust gas recirculation to remaining engine cylinders, it may be possible to improve an engine's torque response. Specifically, torque production of engine cylinders supplied exhaust gas from the dedicated EGR (DEGR) cylinder(s) may be improved since cylinder volume for additional fresh charge (e.g., air and fuel) may be made available if exhaust gas recirculation is limited during an increase in driver demand torque. Additionally, if the engine is turbocharged, turbocharger lag may be reduced since exhaust energy from the remaining cylinders may be increased during the increase in driver demand torque.
The present description may provide several advantages. For example, the approach may reduce turbocharger lag. Further, the approach may improve engine torque response. Further still, the approach may allow an engine to operate more efficiently after a threshold amount of boost has been achieved, thereby increasing engine efficiency after additional boost may be provided to the engine more readily.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.